1. Field of the Invention
This invention relates to a film capacitor and a method of and apparatus for manufacturing the film capacitor.
2. Description of Related Art
Recently, there are increasing demands for reducing electronic parts in size, weight and price while improving the performance. Development of film capacitors is being promoted with a view to providing capacitors smaller in size and improved in performance.
A method of manufacturing conventional laminated film capacitors will be described below with reference to the accompanying drawings.
FIG. 18A shows an ideal construction of a conventional laminated film capacitor.
A capacitor body illustrated in FIG. 18A has one-side-metallized films 1, metallic layers 1a which serve as electrodes, and blank sections or non-metallized portions 3.
Conventionally, the one-side-metallized films 1 are laminated while being shifted alternately (overlapped) in the widthwise direction of the films (by a minimum of about 0.2 mm at present) and are rolled up in order to form film spaces 2 at end surfaces where end surface electrodes for the capacitor are to be formed. The film spaces 2 are thereby formed so that the extent of intrusion of contact layers formed from metallikon as end surface electrodes becomes sufficient, thereby obtaining suitable electrical connection between the end surface electrodes or the contact layers (not shown) and the electrodes 1a of the one-side-metallized films 1 as well as sufficient strength of attachment of the end surface electrodes.
In this method, however, an accurate rolling system is required for rolling up the one-side-metallized films 1, and it is difficult to keep the extent of shifting about 0.2 mm owing to meandering of the films in the case where the width of the films is reduced in order to reduce the size of the capacitor or the thickness of the films is reduced in order to increase the capacitance. Actually, the films are shifted as shown in FIG. 18B. This method, therefore, entails problems of inferior yield stability, a high production cost of the manufacturing apparatus and difficulty in designing a smaller film capacitor. A method of rolling up wide one-side-metallized films having a plurality of capacitor bodies and cutting the thus obtained roll into unit capacitors is advantageous because it enables a high productivity. This method, however, cannot be applied to manufacture of the above-described type of capacitors because it does not enable formation of the film spaces 2. In accordance with the conventional applicable methods, a wide one-side-metallized film having a plurality of capacitor bodies is divided by cutting into unit capacitor bodies, and the divided one-side-metallized films are rolled up to produce capacitors. Therefore the productivity of processes based on the conventional methods is considerably low.
To cope with these problems, a type of method such as the one disclosed in Japanese Laid-Open Patent Publication No. 58-24933 has been developed. In this method, through holes or perforations are formed being spotted in electrode-lead-out portions of wide one-side-metallized films each having a plurality of capacitor bodies. These films are rolled up and a roll thereby formed is cut at the electrode-lead-out portions perpendicularly to electrode-lead-out surfaces thereof, thereby leaving film spaces 2.
This method will be described below with reference to FIGS. 19 to 21.
A one-side-metallized film 1 shown in FIGS. 19 to 21 has a metallic layer 1a, blank sections 3, margin sections defined by a margin width 4, and through-holes 9.
In accordance with this method, the wide one-side-metallized film 1 is formed with a plurality of metallic electrodes 1a and a plurality of blank sections 3a, and a plurality of through holes 9 are provided within pairs of adjacent margin sections of the metallized film 1 defined by the margin width 4, as shown in FIG. 19. A plurality of metallized films 1 thus formed are rolled up while being superposed on each other in such a manner that, as shown in FIG. 20, they are alternately shifted from each other to an extent corresponding to 1/2 of the distance between the pairs of adjacent margin sections. A roll thereby formed is cut at the centers of the pair of margin sections or electrode-lead-out surfaces, thereby dividing the roll into a plurality of mother capacitor bodies each corresponding to the element shown in FIG. 21. Film spaces 2 are thus formed from the through-holes 9 so that the extent of intrusion of contact layers formed from metallikon as end surface electrodes 6 into the end surfaces of each element becomes sufficient, as shown in FIG. 22A, thereby obtaining desired electrical contact between the contact layers and the electrodes 1a of the one-side-metallized films 1 as well as sufficient strength of attachment of the end surface electrodes. Thereafter, each mother capacitor body 5 is cut in the direction perpendicular to the direction in which the margin sections extend, thereby obtaining unit capacitor bodies 51, as shown in FIGS. 22B and 22C. FIG. 22B is a perspective view of the capacitor body shown in FIG. 22A.
This construction, however, entails a problem of difficulty in establishing desired electrical contact between the contact layers and the electrodes 1a of the one-side-metallized films 1. That is, burrs formed at the periphery of the through holes 9 displace the closed films and block the film spaces 2 or, if the thickness of the films is reduced to 2.0 .mu.m or less, the films become slackened due to its flexibility and block the film spaces 2, so that the extent of intrusion of the contact layers formed from metallikon becomes inadequate, resulting in failure to establish the desired electrical contact.
To solve these problems, a method such as the one disclosed in Japanese Laid-Open Patent Publication No. 59-37564 has been proposed. In this method of manufacturing film capacitors, the electrode-lead-out surfaces at which all the end surfaces of the dielectric members are made flush with each other are etched by reverse sputtering to expose electrodes.
In application of this method to the industrial process, there are problems of a high production cost of the manufacturing apparatus, a slow etching speed of the physical etching and, hence, a low productivity. Moreover, in this method, etching is made even to the electrodes, and a high voltage is applied to components of the film capacitor during etching, and accordingly the capacitor is damaged by irradiation of ions or electrons, resulting in failure to obtain desired capacitor characteristics.